1. Field of the Invention
This invention relates to heat exchangers that experience flow induced vibrations. The invention, in particular, relates to plate heat exchangers and fluid flow at the inlet and outlet ports of heat exchangers.
2. Discussion of Related Art
A conventional gasketed-plate-and-frame heat exchanger is formed by a pack of heat transfer plates separated by gasket seals and supported between end covers that form a frame that is typically formed of a stationary cover and a movable cover, which are connected together by fasteners that clamp the heat transfer plate pack between them. The number and size of the heat transfer plates is selected based on the field of intended use of the heat exchanger. The heat transfer plates are arranged in a stacked relationship with interspaces or channels formed between adjoining plates. These interspaces are sealed from the surrounding environment by a weld or flexible seal. One of the covers, or both, is provided with port openings to allow inflow and outflow of heat exchanging fluids. The heat transfer plates have corresponding openings or plate ports that form an inlet port manifold and an outlet port manifold for each fluid through the plate pack.
Typically, two different fluids are designed to flow within the heat exchanger. In operation, the heat exchanging fluids flow separately through the plate heat exchanger in the different channels formed between the heat transfer plates. Alternating channels between plates communicate with one of the inlet and outlet port manifolds so as to define a flow area to conduct one of the heat exchanging fluids between the port manifolds. The other channels between plates communicate with the other inlet and outlet port manifolds to define another flow area to conduct the other heat exchanging fluid. A gasket or weld that is similar to, or part of, the gasket or weld around the remainder of the plates is provided around the alternating ports to create separate fluid-tight flow channels. The alternating heat exchanging fluid paths along the surface of the heat transfer plates adjacent to the channels provide for heat exchange between the fluids. In operation, fluid flows through each inlet port on a stationary or movable end cover to the corresponding inlet port manifold and is then distributed to the channels between the plates where heat exchange is effected. Then, the fluid flows from the channels into the corresponding outlet port manifold and to the outlet port on a stationary or movable end cover.
The heat exchange fluid flowing through the pack of plates can experience relatively high velocities at the inlet and outlet ports and the associated port manifolds. This is especially true in large plate heat exchangers, as used in refineries, for example. In these settings, the port velocities can be as high as 7.6 m/s (25 ft/sec.) This high velocity flow has been shown to induce vibrations in the portion of the heat transfer plates that forms the port manifold, especially in those plates positioned adjacent to the inlet and outlet ports on the stationary or removal covers. Vibration can create stresses that lead to material fatigue and failure.
Flow distributors positioned in port manifolds of heat exchangers are known. However, known flow distributors are used to shift flow to different areas of the heat exchanger or to merely more uniformly distribute flow. For example, U.S. Pat. No. 4,303,124 to Hessari is directed to a tube that may be disposed in the inlet duct or the discharge duct to distribute and collect flow, respectively, along the whole length of the ducts. The tube is disposed in the duct so that fluid may flow around the entire tube, including at the entrance and exit and through open portions in the duct. However, this design does not shield the plates in the pack adjacent to the inlet and outlet ports where the maximum fluid velocity exists.
An example of shifting flow in a heat exchanger is shown in PCT Application WO 00/70292 in which control members permit the flow medium to be guided to different sections in the plate package. However, in this type of arrangement, shifting the flow does not shield the plates immediately adjacent to the repositioned flow inlet or outlet from a high velocity fluid flow.
There is a need for a system to minimize vibrations induced by fluid flow in a heat exchanger. Additionally, it would be desirable to find a solution to the problems related to component fatigue and failure in heat exchangers due to fluid flow, particularly in plate heat exchangers.